Spin diode devices

ABSTRACT

According to various embodiments, a spin diode device may include a magnetic tunnel junction stack. The magnetic tunnel junction stack may include a lower magnetic layer, a tunnel barrier layer over the lower magnetic layer, and an upper magnetic layer over the tunnel barrier layer. The lower magnetic layer may include a lower magnetic film. The tunnel barrier layer comprising an insulating material. The upper magnetic layer may include an upper magnetic film. Each of the lower magnetic film and the upper magnetic film may have perpendicular magnetic anisotropy.

TECHNICAL FIELD

Various embodiments relate to spin diode devices that include a magnetictunnel junction.

BACKGROUND

There is an increasing need for microwave detection devices that arecapable of detecting low power microwaves. Existing solutions, such asspin diodes, typically perform poorly at detecting low power microwaves.In order to improve the performance of spin diodes for low poweroperations, external energy is typically needed to induce resonance inthe magnetic tunnel junction stacks of the spin diodes. However, havingto provide an external source of energy to the spin diodes translateinto an overall larger device size, and limited endurance of the device.Further, the existing spin diodes are only able to harness microwaves ofa single frequency bandwidth. As such, multiples of the spin diodes arerequired to harness microwaves of a plurality of frequency bandwidths.

SUMMARY

According to various embodiments, there may be provided a spin diodedevice. The spin diode device may include a magnetic tunnel junctionstack. The magnetic tunnel junction stack may include a lower magneticlayer, a tunnel barrier layer over the lower magnetic layer, and anupper magnetic layer over the tunnel barrier layer. The lower magneticlayer may include a lower magnetic film. The tunnel barrier layercomprising an insulating material. The upper magnetic layer may includean upper magnetic film. Each of the lower magnetic film and the uppermagnetic film may have perpendicular magnetic anisotropy.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. The drawings are not necessarilyto scale, emphasis instead generally being placed upon illustrating theprinciples of the invention. In the following description, variousembodiments are described with reference to the following drawings, inwhich:

FIG. 1 shows a schematic diagram of a spin diode device according tovarious non-limiting embodiments.

FIG. 2 shows a schematic diagram of a MTJ stack, and illustrates theoperating principle of the spin diode device of FIG. 1.

FIG. 3 shows a schematic diagram of a spin diode device 300 according tovarious non-limiting embodiments.

FIG. 4 shows a schematic diagram of a MTJ stack, and illustrates theoperating principle of the spin diode device of FIG. 3.

FIG. 5 shows a schematic diagram of the spin diode device according tovarious non-limiting embodiments.

FIG. 6 shows a schematic diagram of a MTJ stack and illustrates theoperating principle of the spin diode device of FIG. 5.

FIG. 7 shows an electrical circuit diagram of a microwave deviceaccording to various non-limiting embodiments.

FIG. 8 shows an electrical circuit diagram of a microwave deviceaccording to various non-limiting embodiments.

DESCRIPTION

The embodiments generally relate to spin diode devices that includemagnetic tunnel junctions. The spin diode devices may be spintronicdevices. The spin diode devices may be used in applications such as WiFienergy harvesting, embedded object sensors, microwave imaging formedical or nondestructive testing and microwave sensor in militaryapplications.

FIG. 1 shows a schematic diagram of a spin diode device 100 according tovarious non-limiting embodiments. The spin diode device 100 may includea lower electrode 130 and an upper electrode 140. The spin diode device100 may include a magnetic tunnel junction (MTJ) stack 150 disposedbetween the lower and upper electrodes 130, 140. The MTJ stack 150 mayinclude three general layers, namely a lower magnetic layer 102, anupper magnetic layer 106, and a tunnel barrier layer 104 disposedbetween the lower and upper magnetic layers 102, 106.

The lower magnetic layer 102 may be arranged over the lower electrode130. The tunnel barrier layer 104 may be arranged over the lowermagnetic layer 102. The upper magnetic layer 106 may be arranged overthe tunnel barrier layer 104. The tunnel barrier layer 104 may separatethe lower magnetic layer 102 from the upper magnetic layer 106. Thetunnel barrier layer 104 may be non-magnetic, and may magneticallydecouple the lower magnetic layer 102 from the upper magnetic layer 106.The upper electrode 140 may be arranged over the upper magnetic layer106. The lower and upper magnetic layers 102, 106 may each include atleast one magnetic film that has perpendicular magnetic anisotropy(PMA).

The tunnel barrier layer 104 may include magnesium oxide. In alternativeembodiments, the tunnel barrier layer 104 may include aluminum oxide orother materials suitable for magnetically decoupling overlying layersfrom underlying layers. According to various non-limiting embodiments,the thickness of the tunnel barrier layer 104 may be about 0.8 nm toabout 2.0 nm. The tunnel barrier layer 104 may be sufficiently thin,such that electrons may tunnel through the tunnel barrier layer 104,from the upper magnetic layer 106 to the lower magnetic layer 102, orvice-versa.

According to various non-limiting embodiments, the lower and upperelectrodes 130, 140 may each include tantalum. Each of the lower andupper electrodes 130, 140 may be about 5 nm in thickness.

According to various non-limiting embodiments, the lower and uppermagnetic layers 102, 106 may each include one magnetic film that hasPMA. For example, the lower magnetic layer 102 may include a lowermagnetic film (not shown in FIG. 1) having an equilibrium magnetizationdirection 152 that is perpendicular to a plane defined by the lowermagnetic layer 102. For example, the upper magnetic layer 106 maysimilarly include an upper magnetic film (not shown in FIG. 1) having anequilibrium magnetization direction 156 that is perpendicular to a planedefined by the upper magnetic layer 106. The magnetization direction 152of the lower magnetic layer 102 may be opposite, in other words,antiparallel, to the magnetization direction 156 of the upper magneticlayer 106.

FIG. 2 shows a schematic diagram of the MTJ stack 150, and illustratesthe operating principle of the spin diode device 100. The lower magneticlayer 102, or specifically, the lower magnetic film in the lowermagnetic layer 102, may be structured to have a natural ferromagneticresonance (FMR) frequency f_(L). The upper magnetic layer 106, orspecifically, the upper magnetic film in the upper magnetic layer 106,may be structured to have a natural FMR f_(U). The natural FMR frequencyof a magnetic film refers to the frequency at which the incidentmicrowave radiation and the precessional motion of the magnetizationwithin a magnetic film couples, in the absence of an external magneticfield.

In the presence of a microwave oscillating to frequency f_(L), the lowermagnetic layer 102, instead of the upper magnetic layer 106, may absorbthe microwave energy. The absorbed microwave energy may excite magneticmoment in the lower magnetic film of the lower magnetic layer 102 intoFMR. Consequently, the magnetization direction of the lower magneticlayer 102 may change, for example, from the perpendicular direction 152to a new direction 112. The new direction 112 may include an in-planecomponent 114. The change in direction from the perpendicular direction152 to the new direction 112 may be a slight shift, such that the newdirection 112 is closer to the perpendicular direction 152 than to anin-plane direction.

The magnetization direction of the upper magnetic layer 106 may remainrelatively unchanged, as compared to that of the lower magnetic layer102. The change in magnetization direction of the lower magnetic layer102 relative to the magnetization direction of the upper magnetic layer106 may cause a change in an effective resistance across the MTJ stack150, thereby causing a rectification effect across the MTJ stack 150.The change in effective resistance across the MTJ stack 150 may change amagnitude and/or direction of an electrical current travelling betweenthe lower and upper electrodes 130, 140. The spin diode device 100 maydetect the microwave based on at least one of the magnitude of theelectrical current, the direction of the electrical current, orcombinations thereof.

On the other hand, if the microwave incident on the spin diode device100 is oscillating to frequency f_(U), the upper magnetic layer 106 mayabsorb substantially more of the microwave energy than the lowermagnetic layer 102. The absorbed microwave energy may excite electronsin the upper magnetic film of the upper magnetic layer 106 into FMR.Consequently, the magnetization direction of the upper magnetic layer106 may change, for example, from the perpendicular direction 156 to anew direction 122. The new direction 122 may include an in-planecomponent 124. The magnetization direction of the lower magnetic layer102 may remain relatively unchanged, as compared to that of the uppermagnetic layer 106. The change in magnetization direction of the lowermagnetic layer 102 relative to the magnetization direction of the uppermagnetic layer 106 may cause a change in an effective resistance acrossthe MTJ stack 150, thereby causing a rectification effect across the MTJstack 150. The change in effective resistance across the MTJ stack 150may change a magnitude and/or direction of an electrical currenttravelling between the lower and upper electrodes 130, 140. The spindiode device 100 may detect the microwave based on at least one of themagnitude of the electrical current, the direction of the electricalcurrent, or combinations thereof.

Further, the change in effective resistance of the MTJ stack 150 causedby a change in magnetization direction of the upper magnetic layer 106may differ from the change in effective resistance of the MTJ stack 150caused by a change in the magnetization direction of the lower magneticlayer 102. As such, the spin diode device 100 may also determine theoscillation frequency of the microwave, based on the magnitude anddirection of the electrical current travelling between the lower andupper electrodes 130, 140.

While FIG. 2 shows the magnetization directions of the lower and uppermagnetic layers 102, 106 being opposite, i.e. antiparallel, inalternative embodiments, the lower and upper magnetic layers 102, 106may have the same magnetization direction.

FIG. 3 shows a schematic diagram of a spin diode device 300 according tovarious non-limiting embodiments.

The lower magnetic layer 102 may include a lower magnetic film 312. Thelower magnetic layer 102 may further include a lower coupling layer 314disposed over the lower magnetic film 312, and a further lower magneticfilm 316 disposed over the lower coupling layer 314.

The lower magnetic film 312 and the further lower magnetic film 316 mayeach include cobalt, platinum, and combinations thereof. In alternativeembodiments, the lower magnetic film 312 and the further lower magneticfilm 316 may include various combinations of nickel, terbium, palladium,iron, boron, or other metals, or combinations thereof. The differentelements in the lower magnetic film 312 and the further lower magneticfilm 316 may be alloyed or formed of successive layers, so the lowermagnetic film 312 and the further lower magnetic film 316 mayindependently include a plurality of sub-layers in some embodiments. Themagnetic property of the combined lower magnetic film 312 and thefurther lower magnetic film 316 may be the magnetic property for thelower magnetic layer 102 in embodiments with only two magnetic films inthe lower magnetic layer 102. The lower magnetic film 312 and thefurther lower magnetic film 316 may include pinned layers.

According to various non-limiting embodiments, each of the lowermagnetic film 312 and the further lower magnetic film 316 may include atleast one bi-layer film, for example, a film including cobalt arrangedover or under another film including platinum, for example, a Co/Ptfilm. The lower magnetic film 312 may include a plurality of thebi-layer films, arranged successively in a stack. For example, the lowermagnetic film 312 may include up to six of these bi-layer films, i.e.[Co/Pt]₆. For example, the further lower magnetic film 316 may includeup to four of these bi-layer films, i.e. [Co/Pt]₄. The number ofbi-layer film repetitions required may depend on the target microwavefrequencies. In general, the higher the target microwave frequencies,the more bi-layer films will be required.

Each of the lower magnetic films 312, 316 may be magneticallyanisotropic and may have PMA. The FMR frequency f_(L) of the lowermagnetic layer 102 may depend on the thicknesses of the film includingcobalt film and the other film including platinum. For example, thethickness of each of the cobalt film and the platinum film may be about0.2 to 0.5 nm, for an operating frequency range of about 20 GHz to about60 GHz. In an exemplary embodiment, the bi-layer film stack may include0.4 nm of cobalt and 0.4 nm of platinum.

The lower coupling layer 314 may be an inter-layer exchange couplinglayer that provides an anti-ferromagnetic exchange between the lowermagnetic film 312 and the further lower magnetic film 316. Theanti-ferromagnetic exchange may help reduce or compensate for straymagnetic field effects from the lower magnetic film 312 and the furtherlower magnetic film 316. The lower coupling layer 314 may force themagnetization directions of the lower magnetic film 312 and the furtherlower magnetic film 316 to be antiparallel. By having oppositemagnetization directions, the lower magnetic film 312 and the furtherlower magnetic film 316 may resonate at different frequencies andthereby absorb microwaves of different frequency bandwidths. The lowercoupling layer 314 may include ruthenium (Ru), iridium (Ir), rhodium(Rh), or other materials. In various non-limiting embodiments, the lowercoupling layer 314 may include ruthenium at from about 50 to about 100weight percent, or from about 80 to 100 weight percent, based on a totalweight of the lower coupling layer 314. The thickness of the lowercoupling layer 314 may be about 0.3 nm to 0.9 nm.

The upper magnetic layer 106 may overlie the tunnel barrier layer 104.The upper magnetic layer 106 may include an upper magnetic film 322. Theupper magnetic layer 106 may further include an insertion layer 324 overthe upper magnetic film 322, and a further upper magnetic film 326 overthe insertion layer 324. The upper magnetic film 322 and the furtherupper magnetic film 326 may include pinned layers. For example, theupper magnetic film 322 may include at least one pinned layer, and thefurther upper magnetic film 326 may also include at least one pinnedlayer. The upper magnetic films 322, 326 may have the same composition,or they may have different compositions, and there may be more, less, orthe same number of pinned layers in the upper magnetic films 322, 326.The elements in the upper magnetic films 322, 326 may be present asalloys or as layers of pure material or layers of alloys. The uppermagnetic films 322, 326 may include cobalt, iron, boron, alloys thereof,or mixtures thereof. For example, each of the upper magnetic films 322,326 may include a cobalt-iron-boron alloy, such as Co₂₀Fe₆₀B₂₀. Theupper magnetic films 322, 326 may be magnetically “soft” such that theirspin transfer torque and their magnetization directions may be variable.Each of the upper magnetic films 322, 326 may be magneticallyanisotropic and may have PMA. The thickness of the upper magnetic films322, 326 may each be about 0.3 nm to about 1.2 nm.

The insertion layer 324 may be provided between the upper magnetic film322 and the further upper magnetic film 326. The insertion layer 324 maybe non-magnetic. The insertion layer 324 may provide ferromagneticcoupling between the upper magnetic films 322, 326 and may be thinenough to be amorphous. In alternative embodiments, the insertion layer324 may be crystalline. The insertion layer 324 may include tantalum,molybdenum, tungsten, iron or other components, as alloys, or asindividual elements. According to various non-limiting embodiments, theinsertion layer 324 may be about 0.4 nm in thickness.

The thicknesses of the lower magnetic films 312, 316, and the uppermagnetic films 322, 326 may be critical to achieve PMA and may directlyaffect the natural FMR frequencies of these magnetic films. The naturalFMR frequencies of these magnetic films may determine the operatingfrequencies of the spin diode device 300. The spin diode device 300 maybe configured to detect microwaves that oscillate at frequencies thatmatches or coincides with the natural FMR frequencies of the lowermagnetic films 312, 316. The spin diode device 300 may be configured todetect microwaves that oscillate at frequencies that matches orcoincides with the natural FMR frequencies of the upper magnetic films322, 326.

In general, the FMR frequency, f, of a magnetic film may be determinedas follows:

f = γ(H_(ext) + 4 π M_(eff))

where γ represents the gyromagnetic coefficient of the magnetic filmmaterial, where H_(ext) represents an external magnetic field strength,and where M_(eff) represents the effective PMA strength of the magneticfilm. M_(eff) indicates the amount of external energy that is requiredto the turn the magnetization direction of the magnetic film, fromperpendicular to in-plane.

The spin diode device 100 may operate without the need for an externalmagnetic field, and hence, H_(ext)=0. As such, natural FMR frequenciesof magnetic films may be expressed as:

f = 4πγM_(eff)

In other words, the FMR frequency of the respective magnetic films maybe directly proportional to M_(eff) which depends primarily on theinterface effect and the bulk effect. The interface effect may be causedby orbital deformation due to the breaking periodicity at an interface.The bulk effect may be caused by orbital deformation due to crystalspatial asymmetry. At an interface of a magnetic film, an electron mayhave an additional magnetic energy due to spin-orbit interaction. Thisadditional energy may be substantial such that the direction of theequilibrium magnetization of the magnetic film becomes perpendicular tothe plane, in other words, out-of-plane. The PMA strength of a magneticfilm may depend on a thickness of the magnetic film, its composition,crystallinity structure and the layers that are adjacent to the magneticfilm.

For example, the thicknesses of the lower magnetic films 312, 316 may bein a range of about 2 nm to about 10 nm in order to achieve PMA withnatural FMR frequency, and thereby operating frequency, in the range ofabout 5 GHz to about 40 GHz. For example, the thicknesses of the uppermagnetic films 322, 326 may be in a range of about 1.5 nm to about 3.0nm in order to achieve PMA with natural FMR frequency, and therebyoperating frequency, in the range of about 1.5 GHz to about 20 GHz. Forexample, the thicknesses of the upper magnetic films 322, 326 may be ina range of about 0.4 nm to about 2.0 nm in order to achieve PMA withnatural FMR frequency, and thereby operating frequency, in the range ofabout 2 GHz to about 5 GHz.

The MTJ stack 150 may further include a seed layer 310. The seed layer310 may overlie the lower electrode 130. The seed layer 310 may bedisposed under the lower magnetic layer 102, and also under the lowermagnetic film 312. The seed layer 310 may include platinum. The seedlayer 310 may also include nickel, chromium, ruthenium, tungsten,magnesium, holmium, or terbium in various embodiments. The seed layer310 may be about 5 nm in thickness. The thickness and the material ofthe seed layer 310 need not be limited to those stated above, as long asthe seed layer 310 is able to achieve a crystallized template for thelower magnetic film 312.

The MTJ stack 150 may further include a transition layer 318. Thetransition layer 318 may be provided over the lower magnetic layer 102.The transition layer 318 may overlie the further lower magnetic film316, if it is present in the lower magnetic layer 102. The transitionlayer 318 may be non-magnetic. The transition layer 318 may includetantalum, iron, tungsten, molybdenum, terbium, iron, cobalt, or otherelements, either as alloys or as one or more pinned layers, in someembodiments. The transition layer 318 may serve to break the crystallinestructure from the underlying further lower magnetic film 316 (or otherpinned layer, where more than two pinned layers are utilized). Thetransition layer 318 may be amorphous in some embodiments. Thetransition layer 318 may be thin enough such that a crystallinestructure is not formed, for example, the transition layer 318 may beabout 0.2 nm to 0.5 nm in thickness. The transition layer 318 may benon-magnetic, and the amorphous nature of the transition layer 318 mayallow for the non-magnetic characteristic even in embodiments thatinclude iron, cobalt, or other materials that typically are magnetic.

The MTJ stack 150 may further include a polarizer layer 320. Thepolarizer layer 320 may overlie the transition layer 318. The polarizerlayer 320 may be magnetic. The polarizer layer 320 may include cobalt,iron, boron, alloys thereof, or combinations thereof, which may bepresent as alloys or as individual components, and which may be presentas a single layer or as multiple layers, in various embodiments. Thepolarizer layer 320 may have a crystalline structure that is imparted tooverlying layers in some embodiments, and may improve spin polarizationefficiency in the MTJ stack 150. The polarizer layer 320 may have a facecentered cubic crystalline structure, but other types of crystallinestructures may also be possible.

The MTJ stack 150 may further include a capping layer 330. The cappinglayer 330 may be arranged over the upper magnetic layer 106. The MTJstack 150 may further include an optional top barrier layer 328 arrangedover the upper magnetic layer 106. The capping layer 330 may overlie theoptional top barrier layer 328 where the top barrier layer 328 ispresent. As such, the upper magnetic layer 106 may be sandwiched betweenthe tunnel barrier layer 104 and the top barrier layer 328 inembodiments where the top barrier layer 328 is present. The upperelectrode 140 may overlie the capping layer 330. The capping layer 330may further promote the magnetic anisotropic effect of the MTJ stack150. The capping layer 330 may include one or more of tungsten,magnesium oxide, ruthenium, platinum, hafnium, nickel chromium, or othermaterials, either as alloys or as elements. The capping layer 330 may benon-magnetic, and the composition of the capping layer 330 may depend onthe material of the upper magnetic films 322, 326. The optional topbarrier layer 328 may include magnesium oxide in some embodiments, andthe top barrier layer 328 may be non-magnetic. The capping layer 330 maybe about 0.2 nm to about 2.0 nm in thickness. The top barrier layer 328may be about 1 nm in thickness.

According to various non-limiting embodiments, the spin diode device 300may be fabricated using the same production line and processes as theproduction of MRAM devices. The lower magnetic layer 102 may include asynthetic antiferromagnet (SAF), such that it may be a fixed layer. Theupper magnetic layer 106 may be a free layer.

According to a non-limiting exemplary embodiment, the composition andthicknesses of each layer of the spin diode device 300 are described inthe following. Each of the lower and upper electrodes 130, 140 may beabout 5 nm in thickness and may include tantalum. The seed layer 310 maybe about 5 nm in thickness and may include platinum. The lower magneticfilm 312 may include six repetitions of a bi-layer film including 0.4 nmof cobalt and 0.4 nm of platinum. The lower coupling layer 314 may beabout 0.4 nm in thickness and may include ruthenium. The further lowermagnetic film 316 may include four repetitions of the bi-layer filmincluding 0.4 nm of cobalt and 0.4 nm of platinum. The transition layer318 may be about 0.4 nm in thickness and may include tantalum. Thepolarizer layer 320 may be about 1.0 nm in thickness and may includeCo₂₀Fe₆₀B₂₀. The tunnel barrier layer 104 may be about 1.0 nm inthickness and may include magnesium oxide. The upper magnetic film 322may be about 1.2 nm in thickness and may include Co₂₀Fe₆₀B₂₀. Theinsertion layer 324 may be about 0.4 nm in thickness and may includetantalum. The further upper magnetic film 326 may be about 0.9 nm inthickness and may include Co₂₀Fe₆₀B₂₀. The top barrier layer 328 may beabout 1.0 nm in thickness and may include magnesium oxide. The cappinglayer 330 may be about 1 nm in thickness and may include tungsten.

FIG. 4 shows a schematic diagram of the MTJ stack 150, and illustratesthe operating principle of the spin diode device 300 of FIG. 3. In theembodiment shown in FIG. 3, the lower magnetic layer 102 includes twolower magnetic films 312, 316 separated by a lower coupling layer 314.The magnetization directions of the lower magnetic film 312 and thefurther lower magnetic film 316 may be antiparallel, and these lowermagnetic films 312, 316 may have different natural FMR frequencies. Forexample, the natural FMR frequency of the lower magnetic film 312 may bef_(L1), while the natural FMR frequency of the further lower magneticfilm 316 may be f_(L2). The magnetization directions of the uppermagnetic film 322 and the further upper magnetic film 326 may be thesame, as a result of the interlayer exchange coupling effect mediated bythe thickness and material choice of coupling layer 524. Therefore, theupper magnetic films 322 and 326 may act as a single entity with aresulting single natural FMR frequency f_(U). The spin diode device 300may be configured to detect microwave that oscillates according to anyone of f_(L1), f_(L2), or f_(U). In other words, the spin diode device300 may be capable of detecting microwaves of three differentfrequencies. When the incident microwave has a frequency of f_(U), boththe upper magnetic film 322 and the further magnetic film 326 enter FMRand absorbs at least part of the microwave energy. When the incidentmicrowave has a frequency of f_(L1), only the lower magnetic film 312enters FMR. When the incident microwave has a frequency of f_(L2), onlythe further lower magnetic film 316 enters FMR. Like described withrespect to FIG. 2, when any one of the magnetic films resonate, theeffective resistance of the MTJ 150 changes, which produces arectification effect in the spin diode device 300, that enables the spindiode device 300 to detect the microwave.

FIG. 5 shows a schematic diagram of the spin diode device 500 accordingto various non-limiting embodiments. The spin diode device 500 shown inFIG. 5 may be similar to the spin diode device 300 shown in FIG. 3, withthe exception that the insertion layer 324 is replaced by an uppercoupling layer 524. The upper coupling layer 524 may be similar to thelower coupling layer 314, in its function. The upper coupling layer 524may also be an inter-layer exchange coupling layer, and may serve tomaintain antiparallel magnetization directions for the upper magneticfilm 322 and the further upper magnetic film 326. By having antiparallelmagnetization direction for the upper magnetic film 322 and the furtherupper magnetic film 326, as well as for the lower magnetic film 312 andthe further lower magnetic film 316, the spin diode device 100 may beconfigured to detect microwaves of four different frequencies. In thespin diode device 500, both the upper and lower magnetic layers 102, 106may include SAF. Each of the upper coupling layer 524 and the lowercoupling layer 314 may include ruthenium.

FIG. 6 shows a schematic diagram of the MTJ stack 150, and illustratesthe operating principle of the spin diode device 500 of FIG. 5. Themagnetization directions of the upper magnetic film 322 and the furtherupper magnetic film 326 may be antiparallel, and these upper magneticfilms 322, 326 may have different natural FMR frequencies. For example,the natural FMR frequency of the upper magnetic film 322 may be f_(U1),while the natural FMR frequency of the further upper magnetic film 326may be f_(U2). The spin diode device 100 may be configured to detectmicrowave that oscillates according to any one of f_(L1), f_(L2), f_(U1)or f_(U2). In other words, the spin diode device 500 may be capable ofdetecting microwaves of four different frequencies. When the incidentmicrowave has a frequency of f_(U1), only the upper magnetic film 322enters FMR. When the incident microwave has a frequency of f_(U2), onlythe further upper magnetic film 326 enters FMR. Like described withrespect to FIG. 2, when any one of the magnetic films resonate, theeffective resistance of the MTJ 150 changes, which produces arectification effect in the spin diode device 500, that enables the spindiode device 500 to detect the microwave.

While the spin diode devices 300 and 500 include two magnetic films ineach of the lower and upper magnetic layers 102, 106, it should beunderstood that the lower and upper magnetic layers 102, 106 may includemore than two magnetic films. Each magnetic film may be separated froman underlying magnetic film by a coupling layer similar to the lowercoupling layer 314 or the upper coupling layer 514, or an insertionlayer similar to the insertion layer 324. For example, the lowermagnetic layer 102 may include a further lower coupling layer over thefurther lower magnetic film 316, and a second further lower magneticfilm arranged over the further lower coupling layer. Similarly, theupper magnetic layer 106 may include a further upper coupling or afurther insertion layer over the further upper magnetic film 326, and asecond further upper magnetic film arranged over the further uppercoupling layer or further insertion layer.

The spin diode devices 100, 300 and 500 described above may achievevarious advantages as compared to prior art devices. By having PMA ineach of the lower and upper magnetic layers 102, 106, both magneticlayers may be capable of detecting microwaves with high sensitivity upto −50 dBm by operating in the FMR mode. These magnetic layers may beable to operate in the FMR mode without the need for any externalbiasing energy to turn the magnetization directions to the perpendiculardirections. As such, the spin diode devices are always “ON”, as there isno need to power up the devices with an external current or magneticfield. Further, each of the lower and upper magnetic layers 102, 106 maybe able to harness microwave of at least one frequency. In embodimentswhere the lower magnetic layer 102 and/or the upper magnetic layer 106includes more than one magnetic film separated by an inter-layerexchange coupling layer, the spin diode device may be capable ofsimultaneously detecting or harnessing microwaves of 3 or more differentfrequencies. Each magnetic film in the MTJ stack 150 may be structuredto have a PMA strength that is specific to the desired application. Forexample, M_(eff) equivalent to 800 Oe for harvesting 2.4 GHz microwave,and M_(eff) equivalent to 1650 Oe for harvesting 5 GHz microwave. Thespin diode device may be easy to calibrate for sensing applications, asthe FMR frequency is linearly correlated to the M_(eff), and thereby,the PMA strength of the magnetic films. The spin diode device may alsobe smaller in size as compared to conventional spin diode devices.

According to various non-limiting embodiments, the spin diode devices100, 300, 500 may be capable of detecting microwaves with frequencies inthe range of about 1 GHz to about 100 GHz.

FIG. 7 shows an electrical circuit diagram of a microwave device 700according to various non-limiting embodiments. The microwave device 700may include at least one spin diode 720. The spin diode 720 may includeany one of the spin diode devices 100, 300 or 500. The microwave device700 may further include at least one antenna 702, at least one impedancematching network 704, a direct current (DC) combiner 706, and a DC-DCconvertor 708. The at least one antenna 702 may be configured to receivemicrowave 710. The received microwave may pass through the impedancematching network 704, to reach the spin diode 720. Each set of anantenna 702, an impedance matching network and a spin diode 720 may beconnected in parallel to other similar sets. The DC combiner 706 may beconfigured to receive outputs of each spin diode 720 and may be furtherconfigured to combine their outputs for providing to the DC-DC convertor708, which may be connected to a load 750.

FIG. 8 shows an electrical circuit diagram of a microwave device 800according to various non-limiting embodiments. The microwave device 800may be similar to the microwave device 700, but with a differentconnection of its components. In the microwave device 800, at least oneantenna 702 may be connected to a radio frequency (RF) combiner 806. TheRF combiner 806 may combine the microwave signals received in the atleast one antenna 702 and provide a combined RF signal to an array ofthe spintronic devices 720 through the impedance matching network 704.The output from the array of the spintronic devices 720 may be providedto the DC-DC convertor 708.

According to various non-limiting embodiments, the microwave device 700or 800 may be configured to harness input microwave wave of −10 dBm orsmaller in power. The sensitivity of the microwave device 700 or 800 mayfurther depend on other factors, such as increased microwave loss due toadditional impedance from additional wiring/components.

Aspects of the present invention and certain features, advantages, anddetails thereof, are explained more fully below with reference to thenon-limiting examples illustrated in the accompanying drawings.Descriptions of well-known materials, fabrication tools, processingtechniques, etc., are omitted so as not to unnecessarily obscure theinvention in detail. It should be understood, however, that the detaileddescription and the specific examples, while indicating aspects of theinvention, are given by way of illustration only, and are not by way oflimitation. Various substitutions, modifications, additions, and/orarrangements, within the spirit and/or scope of the underlying inventiveconcepts will be apparent to those skilled in the art from thisdisclosure.

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “approximately”, “about,” is not limited to theprecise value specified. In some instances, the approximating languagemay correspond to the precision of an instrument for measuring thevalue. Further, a direction is modified by a term or terms, such as“substantially” to mean that the direction is to be applied withinnormal tolerances of the semiconductor industry. For example,“substantially parallel” means largely extending in the same directionwithin normal tolerances of the semiconductor industry and“substantially perpendicular” means at an angle of ninety degrees plusor minus a normal tolerance of the semiconductor industry.

The terminology used herein is for the purpose of describing particularexamples only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprise” (andany form of comprise, such as “comprises” and “comprising”), “have” (andany form of have, such as “has” and “having”), “include (and any form ofinclude, such as “includes” and “including”), and “contain” (and anyform of contain, such as “contains” and “containing”) are open-endedlinking verbs. As a result, a method or device that “comprises,” “has,”“includes” or “contains” one or more steps or elements possesses thoseone or more steps or elements, but is not limited to possessing onlythose one or more steps or elements. Likewise, a step of a method or anelement of a device that “comprises,” “has,” “includes” or “contains”one or more features possesses those one or more features, but is notlimited to possessing only those one or more features. Furthermore, adevice or structure that is configured in a certain way is configured inat least that way, but may also be configured in ways that are notlisted.

As used herein, the term “connected,” when used to refer to two physicalelements, means a direct connection between the two physical elements.The term “coupled,” however, can mean a direct connection or aconnection through one or more intermediary elements.

As used herein, the terms “may” and “may be” indicate a possibility ofan occurrence within a set of circumstances; a possession of a specifiedproperty, characteristic or function; and/or qualify another verb byexpressing one or more of an ability, capability, or possibilityassociated with the qualified verb. Accordingly, usage of “may” and “maybe” indicates that a modified term is apparently appropriate, capable,or suitable for an indicated capacity, function, or usage, while takinginto account that in some circumstances the modified term may sometimesnot be appropriate, capable or suitable. For example, in somecircumstances, an event or capacity can be expected, while in othercircumstances the event or capacity cannot occur—this distinction iscaptured by the terms “may” and “may be.”

Combinations such as “at least one of A, B, or C,” “one or more of A, B,or C,” “at least one of A, B, and C,” “one or more of A, B, and C,” and“A, B, C, or any combination thereof” include any combination of A, B,and/or C, and may include multiples of A, multiples of B, or multiplesof C. Specifically, combinations such as “at least one of A, B, or C,”“one or more of A, B, or C,” “at least one of A, B, and C,” “one or moreof A, B, and C,” and “A, B, C, or any combination thereof” may be Aonly, B only, C only, A and B, A and C, B and C, or A and B and C, whereany such combinations may contain one or more member or members of A, B,or C.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The foregoingembodiments, therefore, are to be considered in all respectsillustrative rather than limiting the invention described herein. Scopeof the invention is thus indicated by the appended claims, rather thanby the foregoing description, and all changes that come within themeaning and range of equivalency of the claims are intended to beembraced therein.

1. A spin diode device comprising: a magnetic tunnel junction stackcomprising: a lower magnetic layer comprising a lower magnetic film; atunnel barrier layer over the lower magnetic layer, the tunnel barrierlayer comprising an insulating material; and an upper magnetic layerover the tunnel barrier layer, the upper magnetic layer comprising anupper magnetic film; wherein each of the lower magnetic film and theupper magnetic film has perpendicular magnetic anisotropy.
 2. The spindiode device of claim 1, wherein magnetization directions of the lowermagnetic film and the upper magnetic film are antiparallel.
 3. The spindiode device of claim 1, wherein the lower magnetic film and the uppermagnetic film have different natural ferromagnetic resonant frequencies.4. The spin diode device of claim 1, wherein each of the lower magneticlayer and the upper magnetic layer comprises a syntheticantiferromagnet.
 5. The spin diode device of claim 1, wherein the spindiode device is configured to detect a microwave oscillating at afrequency that matches a natural ferromagnetic resonance frequency ofthe lower magnetic film and further configured to detect a microwaveoscillating at a frequency that matches a natural ferromagneticresonance frequency of the upper magnetic film.
 6. The spin diode deviceof claim 4, wherein a resistance across the magnetic tunnel junctionstack changes when one of the lower magnetic film and the upper magneticfilm absorbs the microwave oscillating at the frequency that matches itsnatural ferromagnetic resonance frequency, wherein the spin diode deviceis configured to detect the microwave based on the change in resistanceacross the magnetic tunnel junction stack.
 7. The spin diode device ofclaim 1, wherein the lower magnetic layer further comprises: a lowercoupling layer over the lower magnetic film, and a further lowermagnetic film over the lower coupling layer, wherein the further lowermagnetic film has perpendicular magnetic anisotropy.
 8. The spin diodedevice of claim 7, wherein magnetization directions of the lowermagnetic film and the further lower magnetic film are antiparallel. 9.The spin diode device of claim 7, wherein the lower magnetic film andthe further lower magnetic film have different natural ferromagneticresonance frequencies.
 10. The spin diode device of claim 7, wherein thelower coupling layer is configured to provide an anti-ferromagneticexchange between the lower magnetic film and the further lower magneticfilm.
 11. The spin diode device of claim 7, wherein each of the lowermagnetic film and the further lower magnetic film comprises at least onebi-layer film, each bi-layer film comprising a cobalt-comprising layerand a platinum-comprising layer.
 12. The spin diode device of claim 11,wherein the at least one bi-layer film of the lower magnetic filmcomprises six bi-layer films, and wherein the at least one bi-layer filmof the further lower magnetic film comprises four bi-layer films. 13.The spin diode device of claim 11, wherein the cobalt-comprising layerranges from about 0.2 to about 0.5 nm in thickness, and wherein theplatinum-comprising layer ranges from about 0.2 to about 0.5 nm inthickness.
 14. The spin diode device of claim 1, wherein the uppermagnetic layer further comprises: an upper coupling layer over the uppermagnetic film, and a further upper magnetic film over the upper couplinglayer, wherein the further upper magnetic film has perpendicularmagnetic anisotropy.
 15. The spin diode device of claim 14, whereinmagnetization directions of the upper magnetic film and the furtherupper magnetic film are antiparallel.
 16. The spin diode device of claim14, wherein the upper magnetic film and the further upper magnetic filmhave different natural ferromagnetic resonance frequencies.
 17. The spindiode device of claim 14, wherein each of the upper magnetic film andthe further upper magnetic film comprises cobalt, iron, boron, or alloysthereof.
 18. The spin diode device of claim 14, wherein a thickness ofeach of the upper magnetic film and the further upper magnetic filmranges from about 0.4 nm to about 2.0 nm.
 19. The spin diode device ofclaim 14, wherein the upper coupling layer is configured to provide ananti-ferromagnetic exchange between the upper magnetic film and thefurther upper magnetic film.
 20. The spin diode device of claim 14,wherein the upper coupling layer comprises ruthenium.